1. Field of the Invention
The present invention is generally directed toward methods for producing graphene particles through an eco-friendly, one-step process involving the controlled detonation of a carbon-containing material with an oxidizing agent. In particular embodiments, the invention involves the detonation of a gas-phase hydrocarbon compound with a source of oxygen at relatively high temperatures to produce pristine graphene nanosheets without the use of catalytic materials.
2. Description of the Prior Art
Graphene is a two dimensional monolayer of sp2 bonded carbon atoms in a hexagonal crystal structure. It has been drawing considerable interest because of its unique physical properties including excellent mechanical strength, high intrinsic carrier mobility at room temperature, and electrical and thermal conductivity comparable to the in-plane value of graphite. These properties open gateways for the potential applications of graphene in technological areas such as nanoelectronics, sensors, nanocomposites, batteries, supercapacitors, and hydrogen storage. Pioneering work for the production of graphene was first done by the micromechanical cleavage of highly ordered pyrolytic graphite (HOPG). However, the low yield makes it unsustainable for large-scale use. Numerous methods for preparation of graphene nanosheets have since been developed including chemical vapor deposition (CVD), ultrasonication-assisted exfoliation of graphene oxide (GO) from graphite oxide in water, epitaxial growth on an electrically insulating surface, solution-based chemical reduction of GO, rapid thermal exfoliation of expanded graphite into graphene, high temperature heating of polymer on metal/insulator surface, and gas-phase plasma synthesis. Notably, the CVD method has been used in a roll-to-roll production of 30-inch monolayer graphene films.
For the production of large quantities of graphene, the modified Hummer's method for the production of GO through chemical exfoliation of graphite to graphite oxide and then graphite oxide to GO has gained much attention due to low-cost and higher yield in comparison to other methods. However, this method is not ideal because the GO produced suffers from some important drawbacks such as poor electrical conductivity due to the presence of epoxide, carboxyl, and hydroxyl groups on the graphene sheets. Further, the reduction of GO to graphene needs insalubrious chemical reductants such as hydrazine or sodium borohydride, and high temperature heating in order to recover the graphitic structure. Moreover, the reduction process cannot completely remove the many structural defects introduced by the oxidation process. A few environmentally friendly processes are available to reduce GO to graphene either by chemical or electrochemical methods, but these give low yield. Thus despite the usefulness of previous graphene synthetic methods, none appear to offer economical, eco-friendly, kilogram scale production of the material.